Nowadays, many operating systems are compatible with an advanced host controller interface (AHCI). The AHCI is an interface specification for a Serial Advanced Technology Attachment (SATA) host bus adapter which Intel Corporation played a central role in defining, and many devices can connect one logical device to each SATA host.
There has been a demand for connecting a plurality of drives to one host bus adapter. A port multiplier which is a standard for satisfying such demand is used to connect a plurality of devices to one host. The host selects an operation object device and issues commands for the selected device. A chip set compatible with such a port multiplier is disclosed in “Marvell 88SE92xx-Product-Brief” (data sheets of Marvell 88SE9220/9230/9235 of Marvell Semi conductor Inc).
In a method using a port multiplier, a host can use a plurality of hard disk drives or the like which can be connected to one host, as one RAID set. However, the host cannot divide the RAID set into a plurality of logical devices (which are identified by different logical unit numbers (LUNs), respectively), and cannot recognize them as independent disks. Consequently, in the above-described related-art case where a host can identify only devices having capacities of 2 TiB or less, even if it is intended to use a RAID set having a capacity exceeding 2 TiB, the host cannot divide the RAID set into logical devices each having a capacity of 2 TiB or less, and cannot recognize the RAID set as devices having capacities of 2 TiB or less. Also, in the related-art case, since the host cannot divide the RAID set into a plurality of logical devices, the host cannot separately manage a system area for an operating system (OS) and a user area by dividing those areas into different logical devices. Also, in the related-art method using a port multiplier, the host divides the RAID set into a plurality of logical devices, and recognizes each logical device as an independent disk. However, the method cannot achieve benefit of the actual configuration of RAID set in improvement of reliability. In other words, the host cannot flexibly set a device configuration.